openethereum/transaction-pool/src/lib.rs

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// Copyright 2015-2017 Parity Technologies (UK) Ltd.
// This file is part of Parity.
// Parity is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// Parity is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with Parity. If not, see <http://www.gnu.org/licenses/>.
//! Generic Transaction Pool
//!
//! An extensible and performant implementation of Ethereum Transaction Pool.
//! The pool stores ordered, verified transactions according to some pluggable
//! `Scoring` implementation.
//! The pool also allows you to construct a set of `pending` transactions according
//! to some notion of `Readiness` (pluggable).
//!
//! The pool is generic over transactions and should make no assumptions about them.
//! The only thing we can rely on is the `Scoring` that defines:
//! - the ordering of transactions from a single sender
//! - the priority of the transaction compared to other transactions from different senders
//!
//! NOTE: the transactions from a single sender are not ordered by priority,
//! but still when constructing pending set we always need to maintain the ordering
//! (i.e. `txs[1]` always needs to be included after `txs[0]` even if it has higher priority)
//!
//! ### Design Details
//!
//! Performance assumptions:
//! - Possibility to handle tens of thousands of transactions
//! - Fast insertions and replacements `O(per-sender + log(senders))`
//! - Reasonably fast removal of stalled transactions `O(per-sender)`
//! - Reasonably fast construction of pending set `O(txs * (log(senders) + log(per-sender))`
//!
//! The removal performance could be improved by trading some memory. Currently `SmallVec` is used
//! to store senders transactions, instead we could use `VecDeque` and efficiently `pop_front`
//! the best transactions.
//!
//! The pending set construction and insertion complexity could be reduced by introducing
//! a notion of `nonce` - an absolute, numeric ordering of transactions.
//! We don't do that because of possible implications of EIP208 where nonce might not be
//! explicitly available.
//!
//! 1. The pool groups transactions from particular sender together
//! and stores them ordered by `Scoring` within that group
//! i.e. `HashMap<Sender, Vec<Transaction>>`.
//! 2. Additionaly we maintain the best and the worst transaction from each sender
//! (by `Scoring` not `priority`) ordered by `priority`.
//! It means that we can easily identify the best transaction inside the entire pool
//! and the worst transaction.
//! 3. Whenever new transaction is inserted to the queue:
//! - first check all the limits (overall, memory, per-sender)
//! - retrieve all transactions from a sender
//! - binary search for position to insert the transaction
//! - decide if we are replacing existing transaction (3 outcomes: drop, replace, insert)
//! - update best and worst transaction from that sender if affected
//! 4. Pending List construction:
//! - Take the best transaction (by priority) from all senders to the List
//! - Replace the transaction with next transaction (by ordering) from that sender (if any)
//! - Repeat
#![warn(missing_docs)]
extern crate smallvec;
extern crate ethcore_bigint as bigint;
#[macro_use]
extern crate error_chain;
#[macro_use]
extern crate log;
#[cfg(test)]
mod tests;
mod error;
mod listener;
mod options;
mod pool;
mod ready;
mod status;
mod transactions;
mod verifier;
pub mod scoring;
pub use self::listener::{Listener, NoopListener};
pub use self::options::Options;
pub use self::pool::Pool;
pub use self::ready::{Ready, Readiness};
pub use self::scoring::Scoring;
pub use self::status::{LightStatus, Status};
pub use self::verifier::Verifier;
use std::fmt;
use self::bigint::prelude::{H256, H160 as Address};
/// Already verified transaction that can be safely queued.
pub trait VerifiedTransaction: fmt::Debug {
/// Transaction hash
fn hash(&self) -> &H256;
/// Memory usage
fn mem_usage(&self) -> usize;
/// Transaction sender
fn sender(&self) -> &Address;
/// Unique index of insertion (lower = older).
fn insertion_id(&self) -> u64;
}